1. Field of the Invention
The invention relates to a backsheet for a photovoltaic module and to a method to prepare such a backsheet.
2. Description of the Related Art
With increasing energy prices and increasing concern over the scarcity and the environmental impact of hydrocarbon fuels, industry is turning to alternative energy sources, such as solar energy.
Photovoltaic (PV) modules, also known as solar modules, are used to produce electrical energy from sunlight. Such modules are based on a variety of semiconductor cell systems (the solar cell) that can absorb light and convert it into electrical energy.
In a typical PV module, the solar cell arrays are positioned between two encapsulant layers, which are further positioned between a frontsheet (upper side of the module facing the incoming light) and a backsheet (back side of the module). The most widely used encapsulant is EVA, i.e. Ethylene Vinyl Acetate.
The backsheet provides weather resistance, UV resistance, moisture barrier properties, low dielectric constant and a high breakdown voltage to the solar cell module. To provide such properties to the PV module, a backsheet comprises a weather resistant film, for example a Tedlar™ film, and/or a polyethyleneterephthalate (PET) film. For example a TPT type backsheet, wherein a Tedlar™ film is laminated on both sides of a PET film, or a TPE type backsheet, wherein a Tedlar™ is laminated on one side of a PET film, while on the other side an encapsulant adhesion layer is provided, are nowadays widely used as backsheet on the market.
Instead of laminating a weather resistant sheet on a support it may be advantageous to coat a weather resistant layer on a support, for example to decrease the cost price of the backsheet. Such a weather resistant layer may be coated from an aqueous or a non-aqueous coating solution. US2009/0151774 for example discloses a backsheet wherein the weather resistant layer is coated on a plastic support instead of laminated.
Typically, the coated layer has to be cured to obtain the necessary weather resistant properties. The curing efficiency may also determine the coating speed of the weather resistant layer, as the coated layer has to be “dry” enough at the end of the coating process to avoid “sticking” when the backsheet is stored on roll.